Contact lenses in wide use today fall into two categories. First, there are the hard or rigid corneal type lenses that are formed from materials prepared by the polymerization of acrylic esters, such as polymethylmethacrylate (PMMA). Secondly, there are the gel, hydrogel or soft type of lenses made by polymerizing such monomers as 2-hydroxyethyl methacrylate (HEMA). Finally, there is a new class of high Dk soft lenses made from polymers comprising silicone-containing monomers and/or macromonomers.
Contact lenses made from silicone-containing materials have been investigated for a number of years. Such materials can generally be subdivided into two major classes, namely hydrogels and non-hydrogels. Non-hydrogels do not absorb appreciable amounts of water, whereas hydrogels can absorb and retain water in an equilibrium state. Regardless of their water content, both non-hydrogel and hydrogel silicone contact lenses tend to have relatively hydrophobic, non-wettable surfaces.
Those skilled in the art have long recognized the need for modifying the surface of such silicone contact lenses so that they are compatible with the eye. It is known that increased hydrophilicity of the contact lens surface improves the wettability of the contact lenses. This in turn is associated with improved wear comfort of contact lenses. Additionally, the surface of the lens can affect the lens's susceptibility to deposition, particularly protein and lipid deposition from the tear fluid during lens wear. Accumulated deposition can cause eye discomfort or even inflammation. In the case of extended-wear lenses, the surface is especially important since extended wear lens must be designed for high standards of comfort over an extended period of time, without requiring daily removal of the lens before sleep. Thus, the regimen for the use of extended-wear lenses would not provide a period of time on a daily basis for the eye to rest or recover from any discomfort or other possible adverse effects due to lens wear during the day.
The patent literature has disclosed various surface treatments for rendering the surface of silicone lenses more hydrophilic and more wettable, including changing the chemistry of the surface layer, coating the surface, and compounding the polymer with additives that subsequently diffuse to the surface. Among chemical surface modification techniques are non-polymeric plasma treatments and corona treatments. The surface of a contact lens can also be modified, at least temporarily and to various degrees, by treatment with contact-lens care solutions.
Solutions that wet the lenses before insertion in the eye are required for both the hard and soft types of contact lenses, at least for non-disposable lens or lenses that are reused at least once after being worn. Surfactant cleaning agents in daily lens care solutions are useful for the removal of lens lipids. Also, the use of enzymes or equivalent protein removing agents has been conventional. With the advent of extended wear lenses, however, in which lenses are worn overnight and even continuously over a plurality of days, the conventional lens care solutions no longer have the opportunity to remove depositions that have accumulated over the day with daily cleaning solutions. Also, because of the hyrdrophobicity of silicone hydrogel materials, they are especially susceptible to the deposition of lipid or lipid-like materials.
It would therefore be desirable to have a solution that could be applied to the eye in order to accomplish cleaning and/or prevent the deposition of lipids or other materials until such time as the lens is removed from the eye and cleaned or disposed.
It does not necessarily follow that cleaning agents that can used in cleaning solutions in which the contact lenses are immersed for several hours or more would be effective when applied in the form of eyedrops. In particular, cleaning agents that are designed to prevent the deposition of lipids on the lens must have an extended effect in conjunction with the lens. At the same time, cleaning agents must be selected that are very safe and comfortable, especially as they would be expected to associate with the lens surfaces. Eye irritation must be avoided.
Ophthalmic solutions for rewetting, lubricating, and/or enhancing wearer comfort by application to the eye or a contact lens while being worn in the eye, are known. Rewetting solutions usually contain a wetting agent in combination with a germicide or preservative, a viscosity builder, and salts that adjust the tonicity of the solutions to make them compatible with the osmolality of tear fluids. Isotonic solutions for improving the comfort of wearing soft contact lenses are known. Such solutions typically may also contain lubricants or demulcents, surfactants, and.or buffers.
For example, U.S. Pat. No. 4,529,535 to Sherman discloses a rewetting solution that is particularly useful for silicone contact lenses, including extended wear lenses. One embodiment includes the combination of hydroxyethylcellulose, polyvinyl alcohol, and polyvinylpyrrolidone. U.S. Pat. No. 4,786,436 to Ogunbiyi discloses a wetting solution comprising collagen and other demulcents such as hydroxylethyl cellulose, methyl cellulose, carboxymethyl cellulose, hydroxypropyl methyl cellulose, hydroxylpropylcellulose and the like.
U.S. Pat. No. 4,748,189 to Su et al. discloses an ophthalmic solution for improving the exchange of fluid in the area outside a hydrogel contact lens in the area underneath the hydrogel contact lens, in order to permit tear exchange to occur, thereby preventing the accumulation of waste matter and debris under the lens. The solution contains a hydrogel flattening agent, for example urea, glycerin, propylene glycol, sorbitol or an amino ethanol. Surfactants that are useful in the solution include poloxamer and tyloxapol. Suitable lubricants include hydroxylethyl cellulose, polyvinylalchol, and polyvinylpyrrolidone.
U.S. Pat. No. 5,209,865 to Winterton et al. discloses a conditioning solution for contact lenses that comprises a combination of a poloxamine and a poloxamer surfactant each having an HLB (hydrophilic-lipophilic balance) of seven or below. The solution according to the invention forms a uniform hydrophilic film on a lens surface for which proteins have very little affinity. As such, a contact lens contacted by the solution is said to have a coating that provides a prophylactic effect to the lens.
U.S. Pat. Nos. 4,436,730 and 4,401,327 to Ellis et al. disclose the use of cationic cellulosic derivatives in contact-lens treating solutions, including the combination of a cationic cellulose such as polymer JR-30M and an ethoxylated glucose such as glucam. In column 4, lines 42-57, Ellis et al. state that the combination of a cationic cellulose material with a PEO (polyethyleneoxide) component such as glucam is particularly advantageous for the reason that the cationic component complexes with the PEO component and the complex more strongly adsorbs on the lens surface. The cationic cellulose polymer and entangled PEO are believed to reach into the aqueous phase to provide cushioning and protein resistance. The invention covered by these patents, however, have been used in products for RGP (rigid-gas-permeable) silicone-containing lenses as compared to soft lenses. There is no mention of such solutions preventing the deposition of lipids on extended-wear lenses made from silicone hydrogels.
In view of the above, it would be desirable to provide an eye-drop solution that can be safely and efficaciously used for both lubricating and/or rewetting contact-lens in the eye and, at the same time, serve to prevent the accumulation of lipids or the like on the contact lens while it is worn in the eye.